1. Field of the Invention
The present invention relates to a light source device and a display device including the same. More specifically, the present invention relates to a light source device that is suitably used in a display device having a non-self-emissive transmission type or transflective type display panel and a display device including the same.
2. Description of the Related Art
A display device having a transmission type or transflective type liquid crystal display panel is generally configured such that a light source device (also called a backlight unit) is disposed on the back side of a liquid crystal display panel. A light source device to be incorporated in this kind of display device has light sources such as cold cathode fluorescent tubes. Light is emitted from the light sources, characteristics of the light are adjusted, and the light is projected to the back side of the liquid crystal display panel. The projected light is transmitted through the liquid crystal display panel, making an image displayed visible on the front side of the liquid crystal display panel.
FIG. 14 is an exploded perspective view schematically showing the configuration of a display device 9 including a direct type light source device. As shown in FIG. 14, the display device (the light source device) 9 includes light sources 91, a reflection sheet 92 arranged to diffusely reflect light emitted from the light sources 91, and optical sheets 93 arranged to adjust characteristics of the light emitted from the light sources 91 and the diffusely reflected light.
The reflection sheet 92 diffusely reflects the light emitted from the light sources 91 in order to make intensity in a planer direction of the light exiting from the light source device 9 uniform and to improve luminance by effectively using the light emitted from the light sources 91. In view of this, the reflection sheet 92 is substantially white in the entire surface and has a surface texture that allows for the diffuse reflection of the light.
In order to achieve image display of high quality, it is preferable to improve a luminance of a bright portion of an image displayed on a liquid crystal display panel 94 and lower a luminance of a dark portion of the image. In other words, it is preferable to improve the contrast ratio. Although the use of the reflection sheet 92 described above can improve a luminance of the bright portion of the image displayed on the liquid crystal display panel 94, it also improves luminance of the dark portion of the image. Thus, the display device (the light source device) 9 using the reflection sheet 92 has difficulty in improving the contrast ratio.
As a prior art literature relating to the present invention, Japanese Utility Model Laid-open Publication No. H01-149622 is cited.